Tuning arrangement for oscillatory circuits



Dec. 2, 1941. 1.. DE KRAMOLIN 2,264,661

TUNING ARRANGEMENT FOR OSCILLATORY CIRCUITS Filed Apri l 25, 1939 Inventor Laclc'szas CZe Kramozlrz 7 Women Patented Dec. 2, 1941 s PATENT orrics Ladislas ole Kramolin, Berlin-Kladow, Germany Application April 25, 1939, Serial No. 269,985 In Germany April 30, 1938 5 Claims.

In the testing of direct current amplifiers, where glow discharge tubes are used for coupling successive stages together, it has recently been found, that there is a marked frequency dependence of the alternating current impedance of such tubes upon the direct current traversing the glow path. Investigations have shown that a glow discharge tube behaves like a resistance connected in series with an inductance, the value of this inductance being dependent on the direct current traversing the glow discharge tube.

Hence, by altering this direct current component, the inductive resistance of the glow discharge tube may be altered.

Recognition of this fact has led to the use of glow discharge tubes of this kind for the purposes of the low frequency transmission regulation of a low pass filter.

Owing to the high inertia of the gas molecules, very high inductance values and restricted ranges of variation are obtained with such tubes for highfrequencies, which bar the use of these tubes in the high frequency range, since it is necessary to work in a region of the glow discharge tube characteristic which represents a negative resistance so that the arrangement readily becomes self-oscillatory.

According to the present invention these drawbacks are obviated by suppressing the oscillating tendency of glow discharge tubes, or by rendering this tendency directly useful for the purposes of the apparatus in question, so that the selfoscillation is not troublesome.

To eliminate the oscillating tendency it is in the first place necessary, as will be clear from what has been said above, to work at points on the glow discharge tube characteristic which either do not present a negative resistance at all or only to a slight extent. To render this device serviceable at high frequencies also there is used in such cases, according to the present invention, for the filling of glow discharge tubes or other gas discharge tubes (e. g. with hot cathode) used for the same purposes, a gas having a very low atomic weight. Amongst gases suitable for this purpose is hydrogen.

A further possible expedient for eliminating saw-tooth oscillations consists in connecting an inductance in parallel to the glow discharge tubes acting as a fixed or variable inductance. It is advisable to give this inductance a value greater than that of the glow discharge tube in order that there may be obtained as large a range of variation of inductance as possible in response to alteration of the direct current in the glow discharge tube.

The connecting of coil and glow discharge tube in parallel may be combined with the use of gases of low atomic weight, such as hydrogen, for the filling of the glow discharge tubes.

Finally, it is also possibl with the glow discharge tubes intentionally to set up oscillations, and in this connection, since glow discharge tubes generally do not have so great a tendency to oscillate at the high frequencies used in wireless work (their inductance being in this case very high) it may be expedient tostimulate oscillation by the use of a separate auxiliary oscillating device.

This last-mentioned expedient can only of course be used when the presence of locally generated oscillations in the apparatus concerned is desirable, as is the case for instance with a superheterodyne receiver.

However, a gas discharge tube which does not itself oscillate, and which acts as an inductance or as a variable inductance, particularly a glow discharge tube, is also suitable for such uses in which it is desirable to set up local oscillation; the reason for this is that if an attempt were made to use a glow discharge tube or other gas discharge tube as tuning means in connection with the tuning of a normal set, the effective resistance present is a seriously disturbing factor.

This resistance widens the resonance curve of the circuits concerned very considerably and thus reduces selectivity to such an extent as to be generally useless under practical working conditions. Nevertheless, the utilisation of the inductance of glow discharge tubes should not be impossible even in particular cases of this kind.

However, if the glow discharge tube or other gas discharge tube is merely used for the tuning of the oscillator circuit alone (the principle of the so-called single-span superheterodyne receiver) or if the gas discharge tube is used, at least in addition to the oscillator circuit, only for tuning the preliminary circuit or circuits, this property is not troublesome, since the intermediate frequency operation of a set of this kind can provide the necessary selectivity by appropriate dimensioning of the component elements. In such cases, even when one or more preliminary circuits which are tunable, for instance simultaneously with the oscillator circuit (single knob operation), are present, it is certainly advantageous to work with high intermediat frequencies, say of 1600 kc. or more, since whistling and the like noises which might otherwise possibly occur owing to defective input selectivity may then be eliminated to a great extent.

Arrangements of this kind are particularly suited for remote tuning, since the relatively small output requisite for feeding the gas discharge tubes with direct current may easily be regulated at considerable distances.

Just as the relatively high self-inductance of a glow discharge tube or the like at high frequencies produces a corresponding step-down transforming effect giving suitable transformation adaptation to any oscillating circuit impedances (in which case the effective impedance enters into the tuning circuit proper to a corre-' spondingly reduced extent, while at the same time, a loose coupling may be desirable between the tuning circuit proper and the circuit containing the glow discharge tube) so may the glow discharge tube also if desired serve as tuning means or as tuning correcting means in such very sharply tuned and slightly damped circuits.

The glow discharge tube is then suitable for instance for purposes of automatic tuning correction or of automatic and manual selectivity regulation.

In the accompanying drawing there is shown an embodiment of the invention for a frequency variable generator, in which a glow discharge tube serves as tuning means. The chain-dotted line in the drawing separates the tuning control device, which maybe disposed at a considerable distance, from the generator proper, which latter may be the control transmitter for a transmitting station or the local oscillator of a superheterodyne receiver, for instance of a single-span superheterodyne receiver.

In an apparatus of this kind there may however be further preliminary circuits tuned in the same way or in any other known way.

In this embodiment V1 denotes the glow discharge tube and V2 a normal oscillator valve. An oscillating circuit LC is connected in the usual manner to the grid circuit of the oscillator valve, and the oscillations are obtained in the usual manner by means of the back-coupling coil L1. The oscillator circuit coil L is provided however with greater inductance than would correspond to the wavelength to be produced, and its value is varied by the tube V1 connected in parallel from the high frequency aspect, by virtue of the arrangement that in this tube V1 the strength of the direct current flowing therethrough is varied by altering the position of the slider at the tuning control potentiometer B.

By arranging the tube V1 and the self-inductance L in parallel, the-generating of saw-tooth oscillations is very considerably reduced. It is expedient for this purpose, that the capacity values of the blocking condensers 'Cl and C2 should be so selected that they do not tend, by reason of their size, to produce saw-tooth oscillations of a frequency which might come near to the working frequencies or of which the working frequencies can form an integral multiple, particularly of a lower order, so that these saw-tooth oscillations are not set up by the working frequencies, if they are not desired in any particular case. In the present example these condensers are for this reason made large relatively to the capacity of the oscillating circuit.

In the annexed claims the term gas or vapor filled glow discharge tube means exclusively a glow discharge tube having a filling of a gas or vapor other than air, and excludes high vacuum electron tubes from which the air has been eX- hausted completelyor to the last traces.

I claim:

1. In a high frequency electrical circuit, an electron tube, inductance and capacity elements of magnitudes for producing high frequency currentthe inductance element comprising a variometer consisting of a gas or vapor filled glow discharge tube and said elements being arranged in a tunable circuit connected to an electrode of said electron tube, means for varying the direct current traversing the discharge path of said glow discharge tube, said means constituting the variometer actuating means to tune said tunable circuit, and stabilizing means for substantially preventing saw tooth oscillations in said tunable circuit.

2. In a high frequency electrical circuit, an electron tube, inductance and capacity elements of magnitudes for producing high frequency current the inductance element comprising a variometer consisting of a gas or vapor filled glow discharge tube and said elements being arranged in a tunable circuit connected to an electrode of said electron tube, means for varying 'thedirect current traversing the discharge path of said'glow discharge tube said means constituting the variometer actuating-means to tune said tunable circuit, and'an inductance connected in parallel with the discharge path of said glow discharge tube.

3'. A high frequency electrical circuit according to claim 1 in which the glow discharge tube has a filling'of a gas of low atomic weight.

4. In an oscillation generator, an amplifier tube, a tunable circuit connected to the grid of said amplifier tube said circuit containing capacity and inductance elements the inductance element including an induction variometer for the tuning of the circuit said variometer consisting of a gas or vapor filled glow discharge tube, means for producing oscillation in said tunable circuit, an inductance connected in parallel with the discharge path of said glow discharge tube, and means for varying the direct current traversing the discharge path of said glow tube said means constituting the variometer actuating means to tune said tunable circuit.

5. A high frequency circuit as claimed in claim 2, wherein the value of the parallel inductance is greater than that of the inductive effect of the discharge tube.

LADISLAS rm KRAMOLIN. 

